Currently, amorphous silicon TFT (a-Si) technology has become the dominant technology in flat panel display industry because it has the advantages over its counterparts, such as, low fabrication temperature, uniform characteristics over large area, low cost and mature process.
In recent years, integrated gate driving circuits with a-Si TFT has attracted great attention in order to further improve the performance of the amorphous silicon TFT LCD and reduce its cost. Conventionally, bonding methods, such as chip on board (COB), tape automated bonding (TAB), chip on glass (COG), etc., have been used to connect peripheral ICs to flat display panels. Compared with such common scheme, integrated gate driving circuits with TFTs can not only reduce the number of external ICs and simplify bonding connections, but also light, thin and symmetrical display panels with narrow bezel is made possible. Therefore, LCD modules will become more compact, reliable with lower cost.
Designing an integrated circuit with a-Si TFT usually faces two problems. One is that the carrier mobility of a-Si is too low to provide large driving current, which lowers the speed of circuit. Another is that a threshold voltage (VT) of a-Si TFT will shift under a long time electric stress, and such VT shift may cause the circuit to be unstable and even disabled.
So far, several solutions of integrated a-Si TFT gate driver to solve these two problems have been reported. The reported circuits usually use gate voltage bootstrapping to enhance the driving ability of a pull-up TFT. And the pull-down TFTs are turned-off every half period by two complementary clocks to eliminate VT shift. These schemes usually use more than ten transistors in one unit. However, there are obvious disadvantages in such gate drivers using two-phase clock, such as high power consumption, poor stability, high circuit complexity etc, which restrict integrated gate driver from being used in high performance applications. For this reason, it is desirable to integrate gate driver with low power consumption and good reliability.